The invention is related to the field of acoustic blankets, and in particular to an acoustic blanket and attachment system referred to herein together as an acoustic blanket system.
Rocket powered space vehicles generally include a launch vehicle portion and payload portion. The launch vehicle portion provides the primary thrust for launching and delivering the payload portion from the earth""s surface into a desired orbit. Acoustic blankets are used on space vehicles to protect the payload and other systems from damage caused by acoustic energy generated by the rocket engines and dynamic pressure. These blankets are passive systems that include an acoustic absorbing material, such as honeycomb or fiberglass batting, disposed within a cover material such as carbon Teflon impregnated fiber glass or an aluminized broad good. The cover material is folded, sewn, and/or taped in various elaborate manners around the acoustic absorbing material to form a blanket of predetermined dimension. The blanket is mounted to the space vehicle, such as on a payload fairing, in a side-by-side relationship with other similar blankets. Separate metallic frames, adhesive, or lacing tape is typically used to attach the blankets to the space vehicle.
Unfortunately, present acoustic blankets suffer from numerous drawbacks primarily related to the manner in which the blankets are constructed and the materials used, thus resulting in heavy, costly, and complicated blanket designs. For example, a typical blanket costs on the order of eight hundred to one thousand dollars to manufacture and can weigh as much as eight to nine pounds per square foot.
Yet another problem with present acoustic blanket designs is that they are often ineffective at lower frequency levels, e.g. below 500 Hz. One solution to this problem is provided by the incorporation of a Helmholtz resonator within the blanket. These resonators, however, add additional costs to the blanket construction and are limited by their sandwich core concept that is susceptible to weaknesses such as delamination of the core/face sheet and moisture retention.
Another problem with present acoustic blanket designs is related to the inadequacy of certain present attachment methods, e.g. adhesives, lacing tapes and complex metallic frames. During flight, it is common for some or all of the blankets to become detached from the launch vehicle and slump, creating a gap between adjacent blankets that permits the transmission of un-dampened acoustic vibrations through the fairing. In addition, because acoustic energy responds differently when transferred through different mediums, it Is often desirable to leave an air gap between the acoustic blanket and the launch vehicle skin. In this case, the frame method of attachment is used to affix the blanket(s) and maintain the air gap. The frame, however, results in additional weight as well as other problems such as dimensional control of the air gap.
The present invention generally relates to an acoustic blanket system and methods for use and manufacturing the same. The present acoustic blanket system and methods are primarily for use with space vehicles, but as will be apparent from the following description, are appropriate for use in other applications requiring attenuation of acoustic energy. Accordingly, it is an object of the present invention to provide a lightweight, low cost, robust acoustic blanket and installation system. Another object of the present invention is to provide an acoustic blanket that is easily fabricated, requires no complicated folding or forming, and minimizes nonrecurring tooling and templates. Another object of the present invention is lo provide an acoustic blanket that is mountable to a surface so as to define an air gap between the blanket and the surface that is tunable to achieve improved acoustic attenuation efficiency. Finally, another object of the present invention is to provide a blanket that is not subject to slumping and repositioning problems during ascent and maximum loading environments.
These objects and other advantages are provided by the present acoustic blanket system, which includes an improved acoustic blanket design and system for connecting the acoustic blanket to a structure, such as a space vehicle fairing. The acoustic blanket may include first and second carbon Teflon impregnated fiberglass cover materials and at least one Polyimide foam panel. The Polyimide foam panel(s) is disposed between the cover materials, which are heat-sealed around at least a portion of their perimeter to form a low mass fully encapsulated blanket.
Various refinements exist of the features noted in relation to the present acoustic blanket. Further features may also be incorporated into the acoustic blanket to form multiple examples of the present invention. These refinements and additional features will be apparent from the following description and may exist individually or in any combination. For instance, the acoustic blanket may be combined with the system for connecting the acoustic blanket to a structure. The system may include a plurality of fastener assemblies that connect the blanket to a structure to define an air gap of pre-determined dimension between the blanket and the structure. The fastener assemblies may include standoffs of varying dimension that are used to achieve precise air gap dimensions. The fastener assemblies also include a mating threaded member to connect the blanket to the standoffs. Grommets installed in the heat-sealed perimeter of the cover materials may also be used to provide reinforcement at the attachment points between the blanket and standoffs. In this regard, the mounting assembly provides dimensional control of the blanket relative to the structure to control the air gap and prevent slumping and/or deformation during maximum loading environments.
The acoustic blanket may also include at least one vent heat-sealed into one of the cover materials for pressure equalization within the blanket. The vent is preferably a relatively fine mesh to prevent particulates from the Polyimide foam core panel from escaping from the blanket and contaminating the surrounding environment.
The acoustic blanket may also include at least one barrier ply layer disposed within the cover materials. The barrier ply may be heat-sealed or mechanically attached along its perimeter to the cover materials. The barrier ply layer is preferably a septum material that exhibits efficient acoustic attenuating properties in the frequency range below 500 Hz. In examples of the present blanket where multiple Polyimide foam panels are included, various tuning options to achieve different acoustic attenuation characteristics for the blanket are provided by varying the thickness of the panels and the position of the barrier ply layer-within the blanket. Since the barrier ply layer does not permit significant acoustic energy transmission between sections of the blanket separated by the barrier ply layer, the barrier ply layer effectively defines an air gap between the barrier ply layer and the skin of the launch vehicle. When multiple panels are utilized, the air gap is easily increased and/or decreased by the location of the barrier ply within the blanket, and specifically between different ones of the multiple panels to achieve different acoustic attenuation characteristics.